66 nylon has a long history and has recently celebrated its 50th anniversary. Over this period many improvements have been made, and there is a continuing need to reduce costs associated with nylon and processing its fibers into garments. The ease and cost of dyeing nylon garments can be an important aspect, especially since, sometimes, improvements are possible with regard to other specific characteristics of the nylon fiber, but may be associated with a reduced affinity for acid dyestuffs; such reduced dye-affinity can decrease the commercial attraction (for certain end-uses) of another improved characteristic that could be achievable by making changes in the production process for the actual nylon fiber.
So, an improvement in dyeability has long been desirable.
Hitherto, it has been expected that the affinity of nylons for acid dyestuffs would be reduced by addition of small amounts of a dibasic acid, such as sebacic acid, as taught, e.g., by Collingwood et al in U.S. Pat. No. 3,534,540.